In the manufacture of semiconductor integrated circuits (IC), opto-electronic devices, and microelectro-mechanical systems (MEMS), multiple steps of thin film deposition are performed in order to construct several complete circuits (chips) and devices on monolithic substrates or wafers. Each wafer is often deposited with a variety of thin films such as, but not limited to, diffusion barrier layers such as binary and/or transition metal ternary compounds; conductor films, such as, but not limited to, tungsten, copper, and aluminum; semiconductor films, such as, but not limited to, doped and undoped poly-crystalline silicon (poly-Si), and doped and undoped (intrinsic) amorphous silicon (a-Si); dielectric films, such as, but not limited to, silicon dioxide (SiO2), undoped silicon glass (USG), boron doped silicon glass (BSG), phosphorus doped silicon glass (PSG), borophosphorosilicate glass (BPSG), silicon nitride (Si3N4), and silicon oxynitride (SiON); low dielectric constant (low-k) dielectric films, such as, but not limited to, fluorine doped silicate glass (FSG), silicon oxide or carbon-doped organosilicate glass (OSG); photoresist films; and anti-reflective-coating (ARC) films comprising organic or inorganic materials.
Materials of particular interest in the semiconductor industry are composite organosilicate films. It is well known that reducing the overall density of the material may decrease the dielectric constant (k) of the material. One method of reducing the density of the material may be through the introduction of pores. Porous composite organosilicate films can be produced by a chemical vapor deposition (CVD) process or other means using a precursor mixture containing a pore-forming precursor or porogen (typically one or more carbon-containing compounds) and a structure-forming precursor (typically organosilanes and/or organosiloxanes). In certain instances, the carbon-containing residues result from the deposition of a structure-forming precursor and a pore-forming precursor. Examples of structure-forming and/or pore-forming precursors are provided for example in U.S. Pat. Nos. 6,846,525; 6,716,770; 6,583,048, and published U.S. Pat. Publication Nos. 2004/0241463; 2004/0197474; 2004/0175957; 2004/0175501; 2004/0096672; and 2004/0096593, which are incorporated herein by reference in their entireties. Once the composite organosilicate film has been deposited, at least a portion of the pore-forming precursor may be removed to provide a porous film.
Examples of structure-former precursors include silica-containing compounds such as organosilanes and organosiloxanes. Suitable organosilanes and organosiloxanes include, e.g.: (a) alkylsilanes represented by the formula R1nSiR24−n, where n is an integer from 1 to 3; R1 and R2 are independently at least one branched or straight chain C1 to C8 alkyl group (e.g., methyl, ethyl), a C3 to C8 substituted or unsubstituted cycloalkyl group (e.g., cyclobutyl, cyclohexyl), a C3 to C10 partially unsaturated alkyl group (e.g., propenyl, butadienyl), a C6 to C12 substituted or unsubstituted aromatic (e.g., phenyl, tolyl), a corresponding linear, branched, cyclic, partially unsaturated alkyl, or aromatic containing alkoxy group (e.g., methoxy, ethoxy, phenoxy), and R2 is alternatively hydride (e.g., methylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, phenylsilane, methylphenylsilane, cyclohexylsilane, tert-butylsilane, ethylsilane, diethylsilane, tetraethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, dimethylethoxysilane, methyltriethoxysilane, methyldiethoxysilane, triethoxysilane, trimethylphenoxysilane and phenoxysilane); (b) a linear organosiloxane represented by the formula R1(R22SiO)nSiR23 where n is an integer from 1 to 10, or a cyclic organosiloxane represented by the formula (R1R2SiO)n, where n is an integer from 2 to 10 and R1 and R2 are as defined above (e.g., 1,3,5,7-tetramethylcyclotetrasiloxane, octamethylcyclotetrasiloxane, hexamethylcyclotrisiloxane, hexamethyldisiloxane, 1,1,2,2-tetramethyldisiloxane, and octamethyltrisiloxane); and (c) a linear organosilane oligomer represented by the formula R2(SiR1R2)nR2 where n is an integer from 2 to 10, or cyclic organosilane represented by the formula (SiR1R2)n, where n is an integer from 3 to 10, and R1 and R2 are as defined above (e.g., 1,2-dimethyldisilane, 1,1,2,2-tetramethyldisilane, 1,2-dimethyl-1,1,2,2-dimethoxydisilane, hexamethyldisilane, octamethyltrisilane, 1,2,3,4,5,6-hexaphenylhexasilane, 1,2-dimethyl-1,2-diphenyldisilane and 1,2-diphenyldisilane). In certain embodiments, the organosilane/organosiloxane is a cyclic alkylsilane, a cyclic alkylsiloxane, a cyclic alkoxysilane or contains at least one alkoxy or alkyl bridge between a pair of Si atoms, such as 1,2-disilanoethane, 1,3-disilanopropane, dimethylsilacyclobutane, 1,2-bis(trimethylsiloxy)cyclobutene, 1,1-dimethyl-1-sila-2,6-dioxacyclohexane, 1,1-dimethyl-1-sila-2-oxacyclohexane, 1,2-bis(trimethylsiloxy)ethane, 1,4-bis(dimethylsilyl)benzene, octamethyltetracyclosiloxane (OMCTS), or 1,3-(dimethylsilyl)cyclobutane. In certain embodiments, the organosilane/organosiloxane contains a reactive side group selected from the group consisting of an epoxide, a carboxylate, an alkyne, a diene, phenyl ethynyl, a strained cyclic group and a C4 to C10 group which can sterically hinder or strain the organosilane/organosiloxane, such as trimethylsilylacetylene, 1-(trimethylsilyl)-1,3-butadiene, trimethylsilylcyclopentadiene, trimethylsilylacetate, and di-tert-butoxydiacetoxysilane.
The pore-former precursor may be a hydrocarbon compound, preferably having from 1 to 13 carbon atoms. Examples of these compounds include, but are not limited to, alpha-terpinene, limonene, cyclohexane, gamma-terpinene, camphene, dimethylhexadiene, ethylbenzene, norbornadiene, cyclopentene oxide, 1,2,4-trimethylcyclohexane, 1,5-dimethyl-1,5-cyclooctadiene, camphene, adamantane, 1,3-butadiene, substituted dienes, alpha-pinene, beta-pinene, and decahydronaphthelene. Further examples of pore-former precursors may include labile organic groups. Some examples of compounds containing labile organic groups include the compounds disclosed in U.S. Pat. No. 6,171,945, which is incorporated herein by reference in its entirety. Yet another example of a pore-former precursors could also be a decomposable polymers. The decomposable polymer may be radiation decomposable. The term “polymer”, as used herein, also encompasses the terms oligomers and/or copolymers unless expressly stated to the contrary. Radiation decomposable polymers are polymers that decompose upon exposure to radiation, e.g., ultraviolet, X-ray, electron beam, or the like. Examples of these polymers include polymers that have an architecture that provides a three-dimensional structure such as, but not limited to, block copolymers, i.e., diblock, triblock, and multiblock copolymers; star block copolymers; radial diblock copolymers; graft diblock copolymers; cografted copolymers; dendrigraft copolymers; tapered block copolymers; and combinations of these architectures. Further examples of degradable polymers are found in U.S. Pat. No. 6,204,202, which is incorporated herein by reference in its entirety.
In certain instances, a single compound may function as both the structure-former and pore-former within the porous OSG film. That is, the structure-former precursor and the pore-former precursor are not necessarily different compounds, and in certain embodiments, the pore-former is a part of (e.g., covalently bound to) the structure-former precursor.
While the deposition process desirably forms thin films on a substrate (typically a silicon wafer), the reactions that form these films also occurs non-productively on exposed surfaces inside of the process chamber leaving a large amount of residues on the chamber walls, the showerhead, and the foreline downstream of the process chamber. These residues typically contain carbon which is referred to herein as carbon-containing residues. Additional species that may also be present include, for example, silicon from the precursor mixture and/or fluorine from exposure to fluorinated gas-based plasmas used for cleaning and/or fluorine-containing precursors. Accumulation of the carbon-containing residues inside the chamber may result in particle shedding, degradation of deposition uniformity, and processing drifts that can affect subsequent depositions. These effects can lead to defects in the deposited structures and device failure. Therefore, periodic cleaning of the process chamber, also referred to as chamber cleaning, is necessary. These residues have to be removed in order to ensure the integrity (uniformity, composition purity, reproducibility) of the composite organosilicate films subsequently deposited. In some cases this carbon-containing residue may be present in the form of oligomers and polymers thus making residue removal more challenging.
Plasma cleaning using fluorinated gas-based plasmas is commonly used to clean the chamber between depositions. Fluorinated gases typically used include NF3, C2F6, CF4, CHF3, F2, and a variety of other species to provide a convenient source of fluorine atoms (F) in a chamber cleaning process. Some types of fluorinated gases are relatively easy to handle since these gases are non-corrosive and unreactive with materials of construction or atmospheric gases under ambient conditions. Process chambers are typically cleaned using a C2F6/O2 or NF3-based plasma etch process. It has been found, however, that plasmas containing fluorinated gases alone cannot effectively remove all of the carbon-containing residues that deposit on the interior surfaces of the process chamber during the co-deposition processes indicated above that are required to produce composite organosilicate materials.